The structure and operation of wireless communication systems is generally known. Examples of such wireless communication systems include cellular systems and wireless local area networks, among others. Equipment that is deployed in these communication systems is typically built to support standardized operations, i.e. operating standards. These operating standards prescribe particular carrier frequencies, modulation types, baud rates, physical layer frame structures, MAC layer operations, link layer operations, etc. By complying with to these operating standards, equipment interoperability is achieved.
In a cellular system, a governmental body licenses a frequency spectrum for a corresponding geographic area (service area) that is used by a licensed system operator to provide wireless service within the service area. Based upon the licensed spectrum and the operating standards employed for the service area, the system operator deploys a plurality of carrier frequencies (channels) within the frequency spectrum that support the subscribers' subscriber units within the service area. These channels are typically equally spaced across the licensed spectrum. The separation between adjacent carriers is defined by the operating standards and is selected to maximize the capacity supported within the licensed spectrum without excessive interference. In most cases, severe limitations are placed upon the amount of adjacent channel interference that may be caused by transmissions on a particular channel.
In cellular systems, a plurality of base stations is distributed across the service area. Each base station services wireless communications within a respective cell. Each cell may be further subdivided into a plurality of sectors. In many cellular systems, e.g., GSM cellular systems, each base station supports forward link communications (from the base station to subscriber units) on a first set of carrier frequencies and reverse link communications (from subscriber units to the base station) on a second set carrier frequencies. The first set and second set of carrier frequencies supported by the base station are a subset of all of the carrier frequencies within the licensed frequency spectrum. In most, if not all cellular systems, carrier frequencies are reused so that interference between base stations using the same carrier frequencies is minimized but so that system capacity is increased. Typically, base stations using the same carrier frequencies are geographically separated so that minimal interference results.
Both base stations and subscriber units include Radio Frequency (RF) transmitters and RF receivers, together “RF transceivers.” RF transceivers service the wireless links between the base stations and subscriber units. The RF transmitter receives a baseband signal from a baseband processor, converts the baseband signal to an RF signal, and couples the RF signal to an antenna for transmission. In most RF transmitters, because of well-known limitations, the baseband signal is first converted to an Intermediate Frequency (IF) signal and then the IF signal is converted to the RF signal. The RF receiver receives an RF signal, converts the RF signal to an IF signal, and then converts the IF signal to a baseband signal, which it then provides to the baseband processor.
The fast growth of the mobile communications market demands multi-band RF transceivers that are small in size, low in cost, and have low power consumption. These market demands require that the architecture of the RF transceiver to be suitable for a high level of system integration on a single chip for reduced cost and miniaturized mobile device size. Low power consumption is very critical for increasing mobile device battery life and is very important for small mobile devices that include small batteries. To meet these design challenges, some RF transmitters now use translational loop architecture to convert the IF signal to an RF signal. Translational loop architectures are useful for constant envelope modulated wireless systems, such as the new generation Global Standards for Mobile Communications (GSM) and General Packet Radio System (GPRS) phones that employ Gaussian Minimum Shift Keying (GMSK) modulation. However, so far, the translational loop architecture has not been successfully applied in systems that employ a non-constant envelope modulation format, such as QPSK for CDMA (IS-95) and US-TDMA (IS-136) standardized systems, for 8-PSK for EDGE standard based mobile devices, and for mobile devices that support other non-constant envelope modulation formats, such as 16 QAM, 32 QAM, 64 QAM, 128 QAM, etc.
Thus, there is a need in the art for a lower power consumption RF transmitter that supports both constant envelope modulation formats and non-constant envelope formats, among other shortcomings of the prior devices.